Composite parts used in the aerospace industry may be comprised of fibers embedded in a matrix material, as for example, epoxy resins. To increase the strength of the component parts new fibers have been developed and used as the reinforcements, such as graphite, boron and KEVLAR. Due to the extreme toughness of the KEVLAR fibers, new methods must be developed to cut these fibers to shape the component parts and to drill and countersink holes in the KEVLAR work pieces to provide holes and attachment points for bolts, screws and rivets. cutter insert which is held in a rotary tool by a cam lock pin. The insert is held precisely in the holder by three alignment surfaces. When the cutting edges of the insert become dull, the insert may be removed and either sharpened or replaced.
The insert of U.S. Pat. No. 4,197,042 was designed for cutting a composite with a graphite fiber matrix. This cutting insert was ineffective in countersinking a hole in or a hybrid composite composed of KEVLAR epoxy and Carbon epoxy. One method that has been tried for cutting holes in composites which utilize KEVLAR fibers or in a hybrid composite, is to use a piece of sacrificial material clamped to the KEVLAR surface to enhance the cutting effect of the insert. Even this method has not been entirely successful.
The object of this invention is to provide a replaceable carbide cutter insert that will cut a countersunk hole in KEVLAR epoxy without the need for sacrificial material and will provide a clean surface without broken or exposed fibers. The inventive insert accomplishes the desired result by providing a straight cutting surface that engages the composite in a shearing action as the tool holder rotates the insert into the workpiece. The cutter insert may be constructed by brazing or fusing a thin layer of polycrystaline diamonds to the carbide body at the cutting edges. The insert may be provided with two cutting surfaces, to define a hole with a double-tapered conical surface.